Offering a powerful, bass-driven stereo sound with greater clarity and improved dynamics are the CX 300-II Precision Black ear-canal phones. The various sizes of ear adapters (S/M/L sizes) provided in the package allow for a personalised fit as well as a high passive attenuation of ambient noise. Also, the asymmetrical cable design ensures a high wearing comfort as you listen on the go. (from Sennheiser.com product page)